A wheel that is capable of sideways movement is shown in U.S. Pat. Nos. 3,876,255 and 6,547,340 both incorporated herein by this reference. Other prior art regarding “omni-directional” wheels includes U.S. Pat. Nos. 6,857,707; 4,223,753; 6,340,065; 4,907,692; 6,394,203; 6,857,707; 4,715,460; 5,374,879; and 3,465,843. These references are also incorporated herein by this reference.
As shown in U.S. Pat. No. 6,547,340, a typical omni-directional wheel includes a hub rotatably mounted to an axle. A number of rollers are mounted to the hub via mounting brackets and the rollers are set at different angles so that as the hub rotates, each roller, when in contact with the ground, is at the same angle relative to the axle (e.g., 45°). A vehicle equipped with such wheels can move forward and backward, sideways, rotate, or any combination thereof, by controlling the rotational speeds of the wheels.
There are several problems associated with typical omni-directional wheels of the prior art. For example, the rollers are typically tapered on one or both ends. The taper causes a variation in the roller's radius within the contact patch. The resultant scrubbing causes increased rolling friction and wear. Small tapered rollers also limit the load carrying capacity of the wheel. If the size of the rollers is increased, then the wheel itself must also be made larger to support the larger rollers. In some implementations, however, a larger wheel cannot be accommodated. Prior art omni-directional wheels also have a limited capacity to traverse obstacles when the wheel travels sideways.